1. Technical Field
The disclosure relates to a back frame structure for a vehicle seat to be provided in vehicles such as an automobile, an airplane, a ship, and a train.
2. Description of Related Art
As one of back frame structures for a vehicle seat, there is such a back frame structure in which a gate-shaped back frame having a generally reverse U-shape in a front view and serving as a framework of a seatback is formed such that upper end sides of a pair of side frames extending in an up-down direction are connected by an upper frame in a bridged manner. A back frame of this type as described in Japanese Patent Application Publication No. 2014-156212 (JP 2014-156212 A) is a back frame for a vehicle seat with a built-in three point seat belt. In the back frame structure of JP 2014-156212 A, an upper end of a high-strength side frame is connected to an upper end of a normal-strength side frame by an upper frame. The high-strength side frame is on a side where a load from a webbing of a seat belt system is directly applied and the normal-strength side frame is on the other side. A webbing guide is attached to the upper end of the high-strength side frame. Further, a lower end side of the high-strength side frame is connected to a lower end side of the normal-strength side frame by a lower pipe in a bridged manner. The webbing guide is a member configured to guide a webbing let out from a webbing winding apparatus disposed inside the seatback so as to extend from a back-face side of the back frame toward a front-face side thereof.